A watermark is an imperceptible or at least difficult to perceive signal embedded into multimedia content such as audio, video, text, still images, computer graphics, or software. The watermark conveys some useful information without disturbing or degrading the presentation of the content in a way that is noticeable or objectionable. Watermarks have been used for the purpose of protecting the property rights of content providers, e.g., by helping to identify the rightful owner of the content. In this case, it should be possible reliably to retrieve the watermark even from content that has been significantly modified or degraded by various causes. The watermark should be resistant to intentional or unintentional removal, counterfeiting, or other tampering without substantial degradation to the content, significantly reducing its commercial value. A watermark should survive innocent processing like compression, decompression, analog to digital and digital to analog conversion, and format conversion (e.g., converting video from NTSC to PAL). The watermark should defy a deliberate attack by a pirate using common signal processing operations. In addition, it must be difficult to counterfeit a watermark; otherwise, watermarks might not be useful, for example, in resolving multiple claims of ownership.
Watermarking technology is divided into three broad categories with different objectives, namely, tracing, copy protection and proof of ownership (copyright protection). Tracing identifies users that sell or give away illegal copies of protected content. Copy protection is implemented to prevent coping (at least, by compliant recorders) of content that contains a watermark denoting that the content should not be copied. Proof of ownership invalidates claims of ownership by anyone other than the legitimate owner of a copyrighted work.
To help trace the illegal redistribution of multimedia content, a watermark can be inserted into the content that contains information, which identifies the source of the copy. This watermark can include information such as the user identification number (e.g., from a smartcard), the serial number of the terminal, the serial number of the content, and the date and time the content was presented or copied. Since the watermark is different for every terminal and every user of the terminal, it must be inserted by the terminal and similar devices (at least, for broadcasted content such as pay-per-view and video on demand). This type of watermark may be recovered off-line by the content provider, service provider, or law enforcement officials.
To provide proof of ownership, the content provider or service provider embeds a watermark into the multimedia content prior to public distribution. The watermark may be embedded into uncompressed or compressed versions of the content (or both). A properly constructed watermark unambiguously identifies the owner of the content. Later, if multiple claims of ownership need to be resolved, only the rightful owner of the content can recover the watermark from each copy of the content claimed to be an original.
Currently proposed watermarking techniques are proprietary and mutually incompatible. A standardized and unified approach would benefit the consumer by allowing interoperability among different content providers, service providers, and terminal equipment. Consistent and dependable methods for content protection also benefit the consumer since it gives content providers and service providers more incentive to provide content. This invention attempts to reap these benefits by placing a wide variety of watermarking techniques into a unified and standardized framework that is incorporated into a terminal compliant. for example, with the currently proposed Open Platform Initiative for Multimedia Access (OPIMA), the framework for which is described in the called for proposals by the OPIMA, dated Jul. 24, 1998. In accord with the OPIMA philosophy, the proposed watermark standard is open and expandable. Standardization and openness are required because proprietary systems discourage the consumer due to a lack of interoperability. For example, deploying a video recorder that will only record content containing a “copying is allowed” watermark is worthwhile only if it can retrieve watermarks inserted by playback devices produced by many manufacturers. In addition, standardization and openness ensure that compliant devices have at least the minimum capabilities required to support the necessary functionalities (including watermarking). Expandability is needed because experience clearly indicates that technology advances rapidly and, in particular, security technology does not remain secure for very long whereas consumer electronics devices may remain in service for more than a decade. Also, new types of content and new technologies, not yet imagined, must be secure and protected.
Application Ser. No. 09/092,898, filed on Jun. 8, 1998, assigned to the assignee of the present invention and incorporated herein by reference, describes a digital watermark system implementing novel “running marks” embedded into “message holes” in a bitstream bearing information, such as audio, video, still pictures, software, etc., for which there is a proprietary interest to be protected. The message holes are in locations in the bitstream, strategically positioned to be impossible or difficult to observe in a frame (when the bitstream comprises a video signal). In an MPEG environment, the message holes are macroblocks each capable of storing one or more carrier bits of data. The running marks are injected into the message hole locations of the bitstream at the time a medium, such as a DVD, is played. The data represented by the running marks identify the serial numbers of the player and DVD, and the time of play. This information is decoded by an enforcement institution that will play back the contents of an unauthorized copy of the DVD to extract the running marks to be used to trace to the copyist.
To make the extraction process more difficult, an unauthorized copyist (pirate) may combine video outputs from a number of video players when a copy is made, so that the running mark information associated with any one player will not be easily read unambiguously. The copending application describes methodology using code division multiple access coding (CDMA) to detect the running marks associated with each single player among running marks associated with all the players used. Each player in this methodology encodes its running mark data using a different low correlation waveform. The example described in the application implements a set of Hadmard-Walsh (HW) waveforms because they are mutually orthogonal and easily generated. During decoding by the institution to extract the running mark information, bits are recovered by performing correlation (inner products) between the received waveform and reference waveforms to decode the running marks and provide source-of-copying information. Since correlation among these waveforms is low, inner product processing extracts the running mark bits correctly in a field of received waveforms from multiple players. The waveform adopted by a player is selected randomly at runtime from a finite set waveforms, to avoid the situation, although rare, where a pirate may use multiple players having the same waveform to make a copy. To additionally make the waveforms more difficult for the pirate to determine, the described methodology includes waveform value scrambling and uses more than one waveform in a bitstream. To preserve the orthogonal property, and reduce the effect of burst error, the waveforms are permuted among different columns first and then among different rows. Storage of the CDMA waveform values (this may be incorporated in a separate security chip), even on a column basis, requires a considerable amount of memory. Placing the storage off chip is complicated, and security in that event is compromised.
Despite that the described system and methodology is an effective means to thwart piracy, an even greater level of security is preferred. No security methodology can be made absolutely immune from defeat by reverse engineering on the part of a committed pirate. However, it is desirable at least to maximize the amount of time it will require a pirate to invade security so that valuable proprietary material, such as a currently popular movie, is not misappropriated early in its commercial lifetime when it is most valuable.
It is also desirable to utilize the bandwidth of the running mark system, described in the copending application, more efficiently and with greater versatility, to enable the system more easily to accommodate changes in software programming and to simplify running mark housekeeping functions.
It is particularly desirable to formulate a variety of watermarking techniques into a unified and standardized framework that may be incorporated into, for example, an OPIMA compliant terminal.